Scale worms are bristle worms that do not look much like worms, as they are flat, broad and often hairy.
As their name implies they are covered by scales along their entire back for protection. They do not bury into the sediment as most other worms and are in fact most common on hard surfaces also unlike other worms.
They are predators with a proboscis with powerful jaws. When they see some innocent prey, they shoot out the proboscis lightning fast and catch the prey with the jaws.